FIG. 5 illustrates an example of an timing transmission for an internal combustion engine, in which a tensioner lever is used to prevent both excess tension and excess slack in a silent chain. The tensioner lever 500 comprises an arm 510, pivotable on a pivot shaft P adjacent one end of the lever, and a shoe member 520, which extends from one end of the arm 510 toward the other end. The shoe is in contact with a portion of chain C on the slack side, i.e., the side at which the chain travels from a driving sprocket S1 toward a driven sprocket S2. The lever is provided with a pad 511, which is engageable with the plunger of a tensioner (not shown), which exerts a force against the lever, urging it against the chain. The slack side of the chain has two free span regions, designated FS, where the chain C is not in contact with the lever, a sprocket, or any other parts, one such region extending from the point at which the chain begins to disengage from sprocket S1 to the point at which the chain first contacts the shoe 520, and the other extending from the point at which the chain disengages from shoe 520 to the point at which the chain is fully engaged with sprocket S2. These free span regions FS ensure a degree of freedom in the path of the transmission chain C. The tensioner lever 500 is described in Japanese patent publication No. 3448122 (page 1, FIGS. 1 to 4)
Chord vibration can occur in the free span regions FS, where the chain is not in contact with other parts. Such vibration produces vibration noise, and can also result in backlash. Backlash, when intensified, causes the chain to impact against the tensioner lever itself, resulting not only in the production of impact noise, but also in increased wear of the shoe of the tensioner lever.
Backlash in the transmission chain can be reduced by increasing the pressing force applied by the tensioner to the chain. However, although such a measure can reduce backlash, it leads to excessive wear of the transmission chain and the shoe of the tensioner lever.
The main object of this invention is to provide a tensioner lever, which can prevent impact noise, vibration noise, and wear damage to the tensioner shoe, by suppressing backlash in the free span regions of the transmission medium.